Liquid crystal displays are characterized to be of high-display quality, thin, low power consumption, low cost, and the like, and are being spread rapidly for various usages. For example, the liquid crystal display devices are employed to various display products of small size such as monitors for mobile phones and monitors for digital still cameras, to various products of middle size such as monitors for notebook personal computers as well as desktop personal computers, monitors for graphic designs and monitors for medical use, and further to various products of large size such as liquid crystal television sets and digital signage monitors.
Recently, there is an increasing demand for improving the display quality of the liquid crystal display of high-end models and high-luminance image quality is being advanced by achieving high definition and high numerical aperture (high transmittance). Under such circumstances, it is desired to achieve a performance which can provide improvement in the uniformity on the display screens and a wide viewing angle property with high contrast and fine color regenerability.
To improve the uniformity of the display screen, it is necessary to uniformalize the orientation of the liquid crystal within the pixel. As a means for improving it, known is rubbingless orientation processing in which an energy beam is irradiated to an orientation film. There are ion beam orientation processing using He atoms and Ar atoms and photo-orientation processing by performing irradiation of UV (Ultra Violet) rays. Especially, the photo-orientation processing is a process that requires no vacuum processing, which is employed to VA (Vertical Alignment) type products and is being studied and developed to be applied to TN (Twisted Nematic), IPS (In-plane Switching) types, FFS (Fringe Field Switching) type, and the like.
The photo-orientation processing cuts the intermolecular coupling of the orientation film by a molecule level and changes the coordinate position of the molecules or couples those by a molecule level according to the incident direction of the irradiated light and the polarization direction thereof to provide effective anisotropy for the orientation of the liquid crystal molecules. Therefore, the orientation of the liquid crystal molecules can be controlled by a molecule level, so that the orientation uniformity is extremely high. Further, the photo-orientation processing does not face the issues such as bright points and dark points caused due to scars and striped orientation unevenness generated by rubbing of a rubbing cloth and foreign matters generated by shavings of a rubbing cloth which may be observed in the rubbing type processing. Therefore, it is particularly effective for achieving high definition. However, relatively high energy irradiation is required with the photo-orientation processing for giving the orientation property in the orientation film, so that it is desired to improve the process of light irradiation, to refine the pixel structure, and to improve the processing capacity by developing the orientation film materials, etc.
As the techniques for acquiring the wide viewing angle property, there are lateral electric field types such as an IPS type and an FFS type. In such types, nematic liquid crystal molecules aligned horizontally are rotated in the horizontal direction by a lateral electric field, with which changes in the image quality in the viewing angle directions caused by rise of the molecule axes can be suppressed so that the viewing angle property can be improved. Further, with the lateral electric field type, compensation can be done with the viewing angle properties of each electrode region through employing a segmented electrode type in which comb-like electrode shape within a pixel is operated by being segmented into two or four regions. This makes it possible to improve the squint colored change property and gradation inversion. Further, the same effect as that of such improvement can be acquired also with a segmented orientation method in which a same comb-like electrode region within a pixel is segmented to regions of different orientation directions. However, with the above-described segmented electrode method and the segmented orientation method, the liquid crystal orientation becomes discontinuous in the boundaries of the electrode regions or the orientation regions. Thereby, disclination lines are generated, which may deteriorates the contrast by light leakage in black display and may deteriorate the luminance by deterioration of the transmittance in white display since an electric field required for rotating the liquid crystal cannot be applied. As a countermeasure for that, it is effective to shield the light by devising the electrode structure, etc. However, it becomes difficult to be applied to high-definition pixels.
As disclosed in Patent Documents 1 to 5 (related techniques) below, the segmented orientation for the TN type is proposed earlier than that of the lateral electric type. FIG. 26, FIG. 27, FIG. 28, FIG. 29, and FIG. 30 below are quoted directly from each of Patent Documents. Thus, reference numerals applied in each of those drawings are effective only in each of the drawings, and are unrelated to the reference numerals of the other drawings.
FIG. 26 shows the technique depicted in Patent Document 1. Patent Document 1 discloses a technique related to a liquid crystal display device including nematic liquid crystal sandwiched between opposing two substrates where electrodes and liquid crystal orientation films are formed and a plurality of picture elements 6 are arranged in matrix, wherein: on each of the picture elements 6, viewing angles of a liquid molecule is segmented into mutually different regions 18, 19; a lower region on the picture element 6 of an arbitrary row and an upper region of the picture element 6 of a next row have a same viewing angle; and a lower region on the picture element 6 of an arbitrary column and an lower region of the picture element 6 of a next column have a same viewing angle. Thereby, the orientation segmented state is stably maintained, so that the contrast unevenness by the viewing angle directions and the contrast unevenness by a pressure can be prevented. In FIG. 26, gate electrodes 13, source electrodes 17, and an active matrix substrate 20 are illustrated.
FIG. 27 shows the technique depicted in Patent Document 2. Patent Document 2 discloses a technique related to a liquid crystal display element including a liquid crystal layer sandwiched between two substrates with surfaces where electrodes are disposed are opposed to each other and a plurality of pixels a are formed and including two regions A and B of different molecule orientation states within a pixel for each pixel, wherein: between neighboring pixels, one of the regions of an arbitrary pixel and a region of another pixel neighboring thereto are arranged to be regions of a same molecule orientation. Thereby, the number of disclination lines generated when the pixel is segmented into the two regions of different orientations is decreased, so that the liquid crystal display element of high quality display can be acquired. In FIG. 27, pixel electrodes 21 and TFT driving elements 22 are illustrated.
FIG. 28 shows the technique depicted in Patent Document 3. Patent Document 3 discloses a technique with which: a twisted nematic layer on a single pixel is segmented into two regions A and B whose orientation directions are different by 180 degrees for widening the viewing angle range; and further light leakage from the boundary of the twisted nematic layers at the time of normally white black display is prevented by using a light-shielding film to achieve high contrast. This makes it possible to suppress deterioration in the contrast of the liquid crystal display device which includes twisted nematic liquid crystal of different orientation directions within a pixel. FIG. 28(a) shows a typical plan layout of color filters R, G, and B, while FIGS. 28(b) and 28(c) show examples where the technique depicted in Patent Document 3 is employed to FIG. 28A and sections 25 shown with wavy lines indicate that one pixel is segmented.
FIG. 29 shows the technique depicted in Patent Document 4. Patent Document 4 discloses a technique for providing a liquid crystal display device which is excellent in the viewing angle property and capable of achieving high-quality display. A picture element includes four-segmented domains D in which first, second, third, and fourth domains (D1 to D4) having mutually different orientation directions of liquid crystal molecules located in the vicinity of the center of the thickness direction of a liquid crystal layer 30 are arranged in this order along a certain direction. A first substrate 10 includes: two first regions A1 exhibiting a restriction force for aligning liquid crystal molecules in a first direction R1; and a second region A2 exhibiting a restriction force for aligning the molecules in a second direction R2 opposite from the first direction R1, which is provided between the two first regions A1. A second substrate 20 includes: a third region A3 exhibiting a restriction force for aligning the molecules in a third direction R3 crossing with the first direction R1; and a fourth region A4 exhibiting a restriction force for aligning the molecules in a fourth direction R4 opposite from the third direction R3. The boundaries between each of the domains (D1 to D4) are extended in a direction that is orthogonal to the orientation direction of each of the domains (D1 to D4). Note that x, y, and p in FIG. 29 show the lengths.
FIG. 30 shows the technique depicted in Patent Document 5. Patent Document 5 discloses a technique which improves the viewing angle dependency of displayed images even when line segments of any directions, monochrome regions, or characters are displayed on a liquid crystal display device. Included therein are: an orientation film 10 in which a first unit orientation region 6 having a first orientation property and a second unit orientation region 8 having a second orientation property different from the first orientation property are disposed in a mixed manner at line and column positions of a matrix; and an orientation film 10 in which the first and second unit orientation regions 6, 8 are disposed in a mixed manner along the straight lines in all directions. This means that a mask suited for forming a plurality of kinds of orientation regions having different orientation properties on the orientation film 10 is used. In FIG. 30, illustrated are orientation regions 12 constituted with the unit orientation regions 6, orientation regions 14 constituted with the unit orientation regions 8, and reference patterns 16 constituted with the orientation regions 12, 14.
Patent Document 1: Japanese Unexamined Patent Publication Hei 08-043826
Patent Document 2: Japanese Unexamined Patent Publication Hei 06-110060
Patent Document 3: Japanese Unexamined Patent Publication Hei 05-224210
Patent Document 4: Japanese Unexamined Patent Publication 2006-085204
Patent Document 5: Japanese Unexamined Patent Publication 2001-305543
However, there are following issues with the related techniques described above.
The first issue is that high-definition of the pixels and the wide viewing angle property cannot be achieved together with the segmented orientation method done by the photo-orientation processing. As the segmented orientation, four-segmented orientation with which the symmetry of the orientation directions of the liquid crystal can be provided is particularly effective in order to improve the viewing angle properties of not only the top and bottom as well as left and right view fields but also the oblique view field. In the meantime, the liquid crystal orientation becomes discontinuous in the boundary areas of the segmented orientation and disclination is generated, so that it cannot be considered as the region effective for display. The area ratio of the region where disclination is generated is increased with respect to the pixel region as the segment number of the segmented orientation is increased or with the higher definition (as the pixel size becomes smaller), which results in deterioration of the display quality and substantial decrease in the numerical aperture.
The second issue of the segmented orientation method done by the photo-orientation processing is that the photo-orientation processing is not effective for achieving high-definition of the pixels and the wide viewing angle property. In order to improve the viewing angle properties of not only the top and bottom as well as left and right view fields but also the oblique view field, four-segmented orientation capable of providing symmetry of the orientation directions of the liquid crystal is particularly effective. The mainstream of a photo-orientation processing method of the segmented orientation is a method which segments a work substrate into a plurality of UV irradiation areas and executes mask exposure on the segmented regions by step feed, and employed is proximity exposure which takes a gap in the order of about several μm to several tens of μm between the mask and the work substrate. In the segmented orientation, in addition to the fact that the region of one orientation direction becomes small, the region becomes still smaller for achieving high definition. Further, spread of the light of the proximity exposure and alignment precision are the issues. Therefore, it is advantageous to set the light irradiation area of the segmented orientation to be large as much as possible. This point is not mentioned in any of Patent Documents.
The third issue is deterioration of the display quality. As disclosed in Patent Documents 1, 2, and 4, in the segmented orientation, same orientation processing is performed on the areas covering over the pixels. However, the orientation processing is executed in the layout that is continuous only in one direction. Thus, display unevenness on the boundaries of the orientation processed sections is visually recognized continuously, thereby deteriorating the display quality. In order to overcome the display unevenness on the boundaries of the orientation processed sections visually recognized continuously, the technique disclosed in Patent Document 5 provides a mask unit in which a plurality of pixel patterns where orientation states vary by a pixel unit or a sub-pixel unit are combined, and executes the orientation processing by that mask unit. However, even though the case of Patent Document 5 is effective for the display unevenness caused due to the continuous orientation processing boundaries, the mask pattern thereof becomes extremely complicated and it is necessary to prepare the mask for each orientation processing pattern. Therefore, efficient orientation processing cannot be performed.
Further, none of Patent Documents discloses a technique for periodically changing a combination of the segmented electrode layout and segmented orientation layout within a pixel at all, so that efficient orientation processing cannot be performed with those.
It is therefore an object of the present invention to provide a liquid crystal display device and a manufacturing method thereof, with which a finer viewing angle property can be maintained even with high-definition pixels and efficient orientation segmenting processing can be performed.